Connection or fastening systems of the sort noted have turned out to be of value when it is a question of quickly producing connections, that are, generally speaking, only acted on by static forces between the components and the panel in such a way that the components may be quickly taken down from the panel again when necessary. The most common sort of fastening device using a pin-like element is one in which a hole is made through the two elements to be joined together with the same hole diameter in the two elements and then a pin or rod is placed through the two holes so that one end part of the pin or the like is seated in one element and the other end part thereof is seated in the other member or element. Such a fastening device based on the use of a pin is more specially of value when the two joined elements are not to be moved in relation to each other. However, when it is a question of parts that may be moved in relation to each other, as for example when one part is turned in relation to the other or the parts are acted upon by dynamic forces, these known fastening systems are of less use, because there is a chance of their working loose. It is more specially for training and demonstration purposes for trainees in engineering and in fields having to do with pneumatic, hydraulic, electronic or fluidic systems that such kits may well be used to make clear the function of the different parts of such systems under true working conditions. Such a training kit will normally be made up of a panel with openings therein into which the parts may be plugged, that is to say a panel or board with holes therein to take up the pins, and the elements or components that may be joined together by lines (i.e. wires or pipes) and thus connected in a circuit with each other. It is more specially when the components to be joined together are fluidic, pneumatic or hydraulic components that the plug-in connections are likely to be heavily loaded, because of the high pressures or high surge pressures that are to be experienced even when the use is only for training purposes.